python-bcrypt: Do not use lld when building with ptests on.

[kraj]

Somehow linker/lld here fails to link ptests with cargo, therefore workaround it by disabling lld when ptest feature is on.

Fixes errors like
note: riscv64-yoe-linux-ld.lld: error: undefined symbol: PyExc_ValueError\nreferenced by bcrypt_rust.a93ef5fbf090e743-cgu.0

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